Magnetic tape recorder with recessed concave tape guide



May 16, 1967 L. D. BARRY 3,320,370

MAGNETIC TAPE RECORDER WITH RECESSED (-JONCAVE TAPE GUIDE Original FiledMay 27, 1952 4 Sheets-Sheet l INVENTOR LEONARD DODGE' BAR/7 Y L. D.BARRY may m, wm

MAGNETlC TAPE RECORDER WTH RECESSIID CONCAVE TAFE GUIDE 4 Sheets-Sheet 2Original Filed May 27, 1952 May L. D. BARRY MAGNETIC TAPE RECORDER WITHREGESSED CONCA'V'E TAFE GUDI 4 She@ tS-Shee t 3 may w, wm

MAGNETIC TAPE RECORDERWITH RECESSED CONCAVE TAPE GULDE Original FiledMay 27, 1952 L. D. BARRY @32993 7@ 4 Sheets-Sheet d kfw/j XC BIASCURRENT MAX, CURRENT HE PDUC M16 C/CU/ T RETURNS ST6/ML S SHOWN M F/G.i2

INVENTOR United States atent ice 3,320,370 MAGNETHC TAPE RECURDER WITHRECESSED CONCAVE TAPE GUIDE Leonard Dodge Barry, Detroit, Mich.,assignor to AmpeX Corporation, Redwood City, Calif., a corporation of'California Continuation of application Ser. No. 78,348, Dec. 27, 1960,which is a division of application Ser. No. 292,013, May 27, 1952. Thisapplication Nov. 27, 1962, Ser. No. 240,284

2 Claims. (Cl. 179--100.2)

This application is a continuation of my copending application Ser. No.78,348, led Dec. 27, 1960, now abandoned, which is `a division ofapplication Ser. No. 292,013, tiled May 27, 1952, now abandoned.

This invention relates to tape recorders and in particular to a methodand means for recording and reproducing signals for television pictures,sound, and other information.

Magnetic tape rrecorders have long been made for recording sound andinformation with accompanying efforts to improve the magnetic mediumyand thereby lower the tape speed or increase the audio frequencyresponse at a given speed. By providing a recorder which transverselyscans the tape together with special circuits for recording andreproducing over a wide frequency range this improved tape recorder isnot only suitable to apply the required audio frequencies to the tape ata much lower tape speed, but it is also designed for recording videosignals which have a frequency range of about to 4 mc. with a linearvelocity of tape Icomparable to present sound tapes.

One object of this invention is to provide a tape `recorder for videosigna-ls by which these signals can be picked up in a televisionreceiver, recorded, and reproduced from the record as often as desiredto be played back on a television picture tube.

A second object is to provide a system of scanning a tape to enable moreinformation to be recordedon a given length of tape.

A third object is to provide a combination sound and video magnetic taperecorder.

A fourth object is to provide a recording system for video whichminimizes critical adjustment, is simple to operate, is convenientlysized, and has tolerances and design suitable for manufacture.

A fifth object is to provide a television recorder which does notinterfere with the viewing of the television program on the picture tubeof the television set from which the video signal is being recorded.

Other objects have been taken into consideration within the limits ofthis invention resulting in further improvements in the art of taperecording disclosed herein.

The development of this invention required consideration of severalproblems.

In accordance with present standards the frequency required to be passedin a video amplifier is 0-4,000,000 cycles/sec. for a high q-ualitypicture. A good picture can be produced with 30-3,600,000 cycles, andthe more limite-d the frequency range the poorer the resolution of thepicture.

The present Imagnetic recording media have a good level output from 20to .about 5000 cycles at 3.75/sec. The output volume is equalized bycircuits to give a practically flat response in this range. Using afigure of 5000 cycles at 3.75/sec. present day tape will record 1333cycles/ inch. The frequency response is directly proportional to thespeed. To record video on tape or wire to include 4 mc. would take 4mc./ 1333=3000" of medium/sec.

As a feature of this invention a rotary wheel or disk is provided havingrecording heads thereon appropriately 3,320,370 Patented May 16, 1967spaced to scan the tape crosswise for recording and pickup at aperipheral speed of approximately 3000"/sec. The tape is curved toconform to the contour of the wheel.

Keeping the size suitable for portability the following exa-imple isgiven to show the relations of dimensions and speeds. Calculations :arebased on accepted television standards providing for interlaced scanning30 frames/ sec., 525 lines/frame, and 0-4 mc. Video frequency response.

The frequency response required of each horizontal video line is:

4,000,000 cy./sec. 525 lines/frames X 30 frames/sec.

Recording Iat high speed the tape should still take 1333 cy./ inch.

Then the tape width required for each horizontal line and retrace is:

254 oy./line 1333 cyanea-0191 /hne A wider tape per horizontal videoline requires a higher peripheral velocity for scanning but would give abetter frequency response and a higher output if needed. A narrowervideo track would give a lower frequency response and output level, butthe peripheral velocity would be less. Allowance for overlap and otherfactors mentioned later requires a wider tape than the line of signal tobe reproduced.

Selecting 8 as the diameter for the wheel the spacing of the magneticheads around the periphery=0.l91.

The retrace takes (0.16 to 0.18) Xpicture width of video track.

Then picture width=P.W.-0.191-0.17 P.W.

The tolerance is i0.01 0.163=i0.0016. This is within standard practiceand is the tolerance of variation for spacing the heads around thewheel.

The number of heads=8 3.1416/0.191=132 heads.

Increasing the width of the tape to include eight horizontal videolines, the number of heads is reduced to sixteen with a slight increasein diameter.

The r.p.m. of the wheel:

To reduce the -r.p.m. to 5000 then requires a dierent number of headsand a larger dia-meter for equal clarity under given conditions.

Number of heads:

525 X 30X 60/(8 5000) :23.6524 heads.

Diameter-:24X 0.191 X 8/3.1416=11.67".

Using ring-type heads with a 0.0005 `gap a width of 0.01" should besufficient for the pole tips vand approximately equal to the width ofline recorded. With a 0.01 spacing between lines to preventdemagnitization where the picture has changed the linear space/linetotals 0.02.

The linear speed of tape=525 30X 0.02/8=39.4"/sec.

This is faster than required for sound recording, and can be reduced ifa narrower pole piece or little or no spacing between lines is found toproduce a satisfactory picture. The spacing between lines is notconsidered a necessity and would not be used if only one horizontalvideo line was recorded per recorded line across the tape Width since,the lines if aligned properly would build up a eld of picture as thecathoderay `does on the tube. The succeeding fields would not beinterlaced on the recording but would be interlaced by the picture tube.

It should be understood that any improvement in the frequency responseof the tape or magnetic heads over present standards would improve thepicture reproduced,

or reduce the r.p.m. or diameter of the wheel for a given quality ofpicture, and improve the sizing and speed ofY the tape and associatedparts.

In the drawings:

FIGURE 1 is a top plan view ofthe improved tape recording mechanism, theenclosure and electrical circuits being removed;

FIGURE 2 is a front elevation of the recorder shown in FIGURE 1;

FIGURE 3 is an enlarged side elevation of the operating lever assemblyin FIGURES 1 and 2;

FIGURE 4 is an enlarged'section View of the tape guide assembly taken online 4-4 in FIGURE l;

FIGURE 5 is an enlargededge view of the wheel in FIGURES l and 2 partbeing broken away to show the coil connections to commutator segmentsand general construction',

FIGURE 6 is a side view of a portion of the wheel shown in FIGURE 5further enlarged and broken away to show details of the magnetic headsand segments;

FIGURE 7 is a plan view of a piece of tape to show the sound and videomagnetic track; portions thereof being labeled. The two fields of thepicture are outlined and labeled thereon to show the sequence in whichthey are recorded;

FIGURE 8 is a block dia-gram of a television receiver with a recorderconnected thereto;

FIGURES 9 and 10 are combination block diagrams and electricalschematics of two variations of the recording circuits;

FIGURE ll is a schematic land block diagram of the reproducing circuits;

FIGURES 12 through 17 are curves representing the signal at successivepoints in the process of recording and reproducing; l

FIGURES 18 and 19 are schematic views of two alternative arrangementsfor scanning the tape.

Referring to the drawings and in particular to FIG- URES 1 and 2, 20 isa supply reel and 22 is a take-up reel for magnetic tape 24, which asseen from FIGURE 1 is inserted between wheel 26 and groove 28 of -guide29. Guide 29 as seen in cross section in FIGURE 4 has retaining sidesand 31 and edge covers 32 and 33 which hold the tape on both sides ofwheel 26 so that the tape will not leave the groove 28 by friction ofwheel 26 when rotating against the tape.,` Guide 29 holds the tapeagainst the periphery of wheel 26, groove 28 being curved to the radiusof the wheel, and guide 29 exerts a light force against the wheel byspring 36 and pivot bar member 38 which being pivoted at two points 40and 41 in line hold the guide 29 against wheel 26 substantially parallelto the axis of the wheel. Guide 29 has an inserted cushioning pad or gap44 at the line of contact ofthe wheeland guide so that when the tape isinserted by pushing guide 29 away from the wheel the tape will have aslight give in contact with the wheel which will save the tape fromexcessive wear and provide close even contact.

An erasing head 46 bears on the tape 24 along groove 28 ahead of thewheel. Spring 48 furnishes the required pressure, and pad 50 insuresgood contact. Head 46 covers the full width of magnetic media.

A sound recording head 52 bears on tape 244v after it passes the wheel.The head magnets are just wide enough to cover the sound track on thetape. Spring 54 provides the desired contact pressure.

The erase and record heads are each supported by pivoted arms 56 and 58respectively. The heads are curved to it groove 28 and help hold thetape in the groove and steady it. The design principles of the heads aresimilar to any used for sound erase or recording. A.C. erase is notobjectionable because slight variations in the tapes longitudinalmagnetism will not effect trans'- verse scanning. The sound could be puton over the whole video track if desired as long as the tilt of thesound recording head is `adjusted to the slant of the transnecting themto the reproducing circuits.

verse scanning and the proper biasing and limiting of the amplitudeofthe signals is used.

Wheel 26 is driven by constant speed motor 60 through coupling 62, shaft63, spur gear 64 engaging spur gear 66, shaft 68 to which wheel 26 isfixed. Gears 64 and 66 increase the speed to shaft 68. Gear 64 ispreferably a fiber gear as should one of every gear set to reduce noiseand vibration. Guard 69 encloses most of wheel 26. Spring washer 70prevents axialmovement of wheel 26.

Tape 24 is driven by motor 60 through beveled gears 71 and 72, shaft 74,worm 76, worm gear 78 xed on shaft S0 coupled to shaft 82 by a frictionclutch 84, and sprocket tooth drive wheel 86 having teeth which engageholes 88 in tape 24. The tape is moved by this tape transport from leftto right during record and playback at a speed having a fixedrelationship to the r.p.m. of the wheel 26. Thereby recordings can bereproduced even with slight variation inmotor speed.

The take-up reel is driven by its motor 90 during record and playback.The supply reel is driven at a relatively high speed for rewind by itsmotor 92. This practice is followed in some quality tape recorders.

Lever 94 provides means for the operator to shift from a neutralposition N to either a position for record and .playback F in whichlever 94 is shown or a position for rewind R. FIGURE 3 shows the detailsof lever 94. This lever is pivoted about bearings 96 and 98 on shaft100. The lever has four parallel arms extending to bearings 102 and 103holding shaft 80vand bearings 105 and 106 holding shaft 82. Shaft 82 hasthe sprocket drive 86 fixed thereon. The friction clutch 84 heldtogether by spring 108 permits slippage whenever worm gear 78 is engagedwith worm 76 upon the operator moving lever 94 to position F or wheneverthe force to pull the tape exceeds a safe limit. The amount of slippage-decreases until the tape gets up to speed.

When lever 94 is brought to positions N and R lever 110 moves guide 29away from wheel 26 disengaging the tape from the wheel. Lever 110 isactuated by link 112 to lever 94 and bears on 38 in positions N and R.

Lever 94also actuates switches, not shown, to control power to thereelingmotors `90 and 92. The usual switching and safety features should-be provided.

Wheel 26,- as seen in FIGURES 5 and 6, is composed of two nonmagneticdisks 116 and 117 bolted together with bolts 118'. Disk 117 is brazed orotherwise secured to shaft 68. Recording-reproducing heads 120 aresymmetrically spaced. about the circumference of wheel 26 in a space 122provided by grooving the adjoining faces of each disk. Each head has twocoils 124 and 125. The two coils are connected series aiding and theends brought toindividual commutator segments arranged in two concentricrings 126 and 127V around the side of the disk 116. T-he coils aresimilar and similarly connected to the insulated segments so that anysignal recorded or picked up will have the same polarity and valueindependent of which head recorded or picked it up. The cores 128 are intwo parts to facilitate winding and are securely fastened to disk 116 byscrews 129 through overlapping parts of the cores 128. Copper brushes132 and 133 engage concentric rings 126 and 127 respectively to carrythe signals -between the coils and the recording-reproducing circuits.The commutator segments and brushes I prefer to call electricalswitching means.

When in reproducing a head comes in or out of contact with the magneticmedium at the ends of the line being scanned the coils receive a voltagesurge from any magnetization from the signal, bias, or erase that ispresent. This is not part ofthe signal to be picked up; it is adiscontinuity which -has caused this surge. Therefore the signal isrecorded with enough, overlap in scanning successive lines to providefor the period of this voltage surge to end before the coils arecontacted by the brushes con- This is easily doneby changingto anarrower set of brushes than were used for recording or by usingseparate coils and a commutator ring for pickup with brushes having the`desired coverage. A slip `ring could provide a common for one side ofall coils. The recording should be made with sufiicient overlap so thatthere will still be a slight amount of overlap with the narrower brushesto prevent an open circuit interruption of the signal.

FIGURE 7 shows the tape 24 as it would pass under the heads shown inFIGURE 6. The tape has a sound and a video track so labeled. Fields 1and 2 follow in sequence and are composed of a suitable number ofhorizontal lines of video per line of Width labeled REPRO- DUCED SIGNAL.To pick up this REPRODUCED SIGNAL the video track includes Alignment ANDCON- TACT ALLOWANCE that is an overlap provided for the distancerequired by the brushes to come from no contact to suflicient contactwith the segments and allowance for tolerance in spacing heads,commutator segments, positioning of guide 29, and other variables. Thisoverlap added at the entrance and exit of the REPRO- DUCED SIGNAL equalsthe PICKED UP SIGNAL. Adding VOLTAGE SURGE ALLOWANCE gives the requiredminimum RECORDED VIDEO SIGNAL per transverse line. The magnetic mediumcan be wider than this minimum width.

Referring to FIGURES 8, 9, and 10, the recorder picks up a signal at theoutput of the video detector where it has been rectified and ltered ofthe LF. carrier. The recorder is preferably provided with its own videoampliiier with circuits designed to give any desired preemphasis as insound recorders to balance the response over the frequency range. Thesignal is put in the video amplifier. The output thereof is connected toa D.C. restorer, FIGURE 9, as required if the circuits of the videoamplier do not pass the D C. component and so that the signal might alsobe picked up after any TV video amplifier as indicated by -dash lines,FIGURE 8. In FIGURE l the D.C. restorer was omitted. The signal is nextfed to a novel amplifier one form of which is shown in FIGURE 9 andanother form in FIGURE 10.

Referring to FIGURE 9, the signal is then applied to the grid of tube140. A voltage supply Blf-iis connected to the plate of tube 140 throughresistors R1 and R2. R1 being connected between Blfeland a junctionpoint J1. The circuit ofthe head coils 124 and 125 is connected bysegments 126 and 127 respectively engaging brushes 132 and 133 acrosspoints J1 and B2+ in series with an equalizing network represented by acondenser C1 and resistor R3 in parallel. B2'-|- has a potential equalto or less than B1-{-. Grid bias is provided for tube 140 across R4.

, The input signalwould probably vary from 0 to -75 volts. The zerovoltage signal on the grid would represent a White picture in the TV-cathode ray tube and -50 to 75 volts rblack. Tube 140 is fullyconducting with zero grid volts and decreases in conductivity linearlyfrom 0 to -75 volts. I1 is at a minimum potential for this point whentube 140 is fully conducting and maximum when tube 140 is nonconducting.The difference in potential between J1 `at max. and min. can be adjustedby varying R1, R2, and B2| so that the current through coils 124 and 125can vary -as desired. Adjustment can be made to give varying D.C., A.C.with a D.C. cornponent, or pure A.C. Varying D.C. can thus be providedhaving the proper D.C. bias for recording. `Or using an A.C. biasoscillator of high frequency the adjustment is made to provide A.C.alone.

The A.C. bias frequency should be several times the maximum recordedfrequency. Since the tape takes at least a biasingfrequency of 30,000cy. recording 5000 cy.; the tape should take 6X4 mc.=24 m-c. bias forrecording 4 mc. Therefore an A.C. biasing oscillator is shown in blockdiagram with an adjustable resistor R5 to select the best biasingcurrent. The oscillators output 6 circuit is tuned by a smallcapacitance C2 and inductance L to prevent shorting of the signalthrough the oscillator.

Referring to FIGURE 10, this circuit for driving the coils differs fromthe circuit in FIGURE 9 in that' two tubes are used in place of and acomplete bridge circuit is formed. The bridge is formed .by tube inseries with resistor R10 and tube 152 in series with resistor R11 inopposite legs of the bridge, the plate side ends of the legs of bothtubes 150 and 152 connected together by a third leg containing resistorR12, and the cathode side ends of the legs connected together as thefourth leg containing resistor R13. The plate side of the leg of tube152 is connected to Voltage BIH- and the cathode side of the leg of tube150 is grounded to B3\-. Coil 124 with equalizing circuit represented byC3 and R14 is connected as a bridge from the plate side of the legcontaining tube 150 to the cathode end of the leg containing tube 152.The tubes are pentodes or triodes and have their grids connected to theinput signal and biased to a negative potential B4 connected to thegrids by a high resistance R15.

When the tubes are full conducting with zero grid voltage, for example,current iow is from BB-lto B3- through tube 152, R11, coil 124', R10,and tube 150 in series. The tubes decrease in conductivity linearly asthe grid voltage swings from 0 to -75 volts and as they do the potentialacross the .bridge changes linearly. The polarity and potential acrosscoil 124 is determined for a given signal input according to the biasingof the grids, tube characteristics, and values selected for theresistors. The plate voltage is high enough to provide linear operation.Thus varying D.C., A.C. with a D.C. component, or pure A.C. can beprovided. The proper values being selected according to whether A.C. orD.C. biasing is used as with the circuit in FIGURE 9 Steps in theprocess of recording and reproducing a signal are shown by reference toFIGURES l2 through 17.

FIGURE l2 shows a typical signal from the TV detector, not to scale.

FIGURE 13 shows the output from an odd number of amplier stages thusreversing the signal, the D.C. voltage component being restored by theD.C. restorer if it was missing at input or lost in the video amplifier.

FIGURE 14 shows the signal as recorded with D.C. biasing, the polarityof the bias voltage being such -as to reduce the magnetization left bythe saturating erase inagnet. If a minus voltage was used for biasingthe tape the zro reference line would be at the top by an equal distanceabove the bias voltage line. The MAX. and MIN. lines represent therecording current at limits of linearity of recording on the magneticmedium.

FIGURE l5 shows the signal with D.C. components removed ready forrecording with A.C. biasing.

FIGURE 16 represents the net signal recorded with either A.C. or D C.biasing. The iinx lines are omitted for simplicity. The flux density isindicated by the distance the curve departs from the zero referenceline. The ux lines if shown would loop from the vertical faces only.Lines through the zero reference represent cornplete reversal of thedirection of magnetization as indicated by the letters N and S.

FIGURE 17 shows the signal voltage picked up by the coils. Each increaseof magnetization in one direction induces a voltage of one polarity, andeach decreases or reversal of magnetization therefrom induces a voltageof the opposite polarity in the coils. The intensity of this inducedvoltage in either case is proportional to the rate of change of fluxlinking with the coils.

The circuit shown in FIGURE 11 is a practical means developed toreproduce the original signal. This circuit receiving these intermittentvoltages adds and subtracts charges in accordance with the voltageinduced with reference to a linear rate of charging and dischargingcondenser C4. The amplifying portion of this circuit is assumed to bedesigned to supply post-emphasis.

Referring to this circuit, two similar tubes 160 and 161 are provided.One end of the pickup coil 124" is connected to the grid of tube 160 andthe other end connected to the grid of tube 161. Equally matchedresistors R21 and R22 connected in series across the grids of tubes 160and 161 provide a balanced grid bias voltage from a source of negativepotential B-. The cathodes of tubes 160 and 161 are grounded, and theplates are connected in series with equal resistances R23 and R24respectively to B6-ivoltage supply. The plates of tubes 160 and 161 arealso connected to the grids of tubes 164 and 165 respectively in serieswith condensers C5 and C6 respectively. Grid leak bias is provided fortubes 164 and 16S by resistors R25 and R26 respectively. The cathode oftube 165 is grounded through R27 and the plate connected to the cathodeof tube 164. The plate of tube 164 is connected in series with resistorR28 to a positive ypotential B74-, The plate of tube 165 is connected tocondenser C4 in series with a current limiting resistor R29 to form anintegrating circuit. The other side of C4 is grounded. The output acrossC4 is fed to the grid of a video amplifier providing if desired furtherpost-emphasis from which the signal is returned to the TV ahead of itsvideo amplifier as seen in FIGURE 8. The circuit connecting therecorders output to the TV has a high resistance R30 in series toprevent excessive Icurrent caused by improper connection or operation.The connecting leads should be fused where the recorder is to be aseparate unit connected and disconnected from the TV set.

A voltage induced in coil 124" will place opposite charges on the gridsof tubes 160 and 161. The bias voltage supplied -by BS- will be suchthat the tubes 160 and 161 will operate as class A amplifiers. When nosignal is being received condensers CS and C6 have equal charges and thebiasing can be such that tubes 160 and 161 conduct. A signal will causeon tube to conduct more and the other less according to the polarity ofthe signal. The tube which conducts less increases the charge on itsplate condensers and this increases the positive value of the grid ofthe associated tube 164 or 165 causing this tube to conduct if biased tocutofr with no signal or to conduct to a greater extent if not biased tothat extent.

With a sufficiently high voltage applied at B7+, tube 164 conducts,charging the upper plate of capacitor C4 positive and the plate of tube165 positive until tube 165 becomes conductive. A- positive signal(reduction of negative charge) on the grid of tube 165 will causeconduction, reducing the positive charge on the upper plate of C4 andthe cathode of tube 164 enabling tube 164 to be more readily conductivewhen its grid receives a positive charge, thus capacitor C4 gains andloses charges above and below its initial charge. The signal isalgebraically integrated on condenser C4 in that both positive andnegative charges are added thereon, the negative being subtracted fromthe positive.

Tubes 164 and 165 will be biased to the same point of conductivity withno signal and are preferably biased to cutoff with no signal. Thus whena signal increases the grid potential of tube 164 that tube conductsVand increases the potential on C4.` When a signal of reverse polarity isreceived this increases the grid potential of tube 165, and that tubeconducts and decreases the potential on C4. Thus the charge on C4 can beadded and subtracted. The circuit is balanced to add and subtractcharges on condenser C4 on a linear basis, whereby the output voltageacross C4 is proportional to fEdt of the applied signal voltage whichwill be pure A.C. as seen from FIGURE 17 and therefore balance out thesignal charge on C4. The effect of a signal charge on C4 in influencingconductivity can be made negligible. The cathode of tube 165 can beconnected to a negative potential below ground if this is founddesirable to enable 8. it to have a suicient potential differencebetween plate and cathode to conduct.

The circuits for the sound are similar to present-day sound taperecorders-and are therefore not shown.

When reproducing a recorded signal on a TV receiver the lines ofrecording are synchronized with the scanning of the tape by retardingthe tape manually by applying a slight force to slipping clutch 84,FIGURES 1, 2, and 3, until the wheel 26 scans on the lines and notbetween lines if the recording was made with space between lines;otherwise this adjustment is not necessary. The magnetic head scanningwheel 26 should be free from wobble and vibration, and is held againstaxial movement as described so that the path of the magnetic headstherein will not vary beyond allowable tolerances.

Two variations in the arrangement for scanning are shown in FIGURES 18and 19. Other methods of scanning the tape with transverse movementinclude a reciprocating head or heads, and heads mounted on and moved byendless belt.

FIGURE 18 shows two tapes 24 and 24 being scanned by wheel 26 the headsthereof being located on the side in a ring contacting the tapes andconcentric with the axis of the wheel. The resulting transverse scanwill be curved to the radius of the circle of the heads and will enablea slightly longer transverse line for a given width of tape than withthe scanning wheel rotating perpendicular to the face and edge of thetape. The tape is at when scanned. Rollers and 181 hold the tapes 24 and24 respectively against the heads on wheel 26. Two or more tapes can besimultaneously scanned by one wheel and two or more recording andreproducing circuits provided. Some applications are the making ofseveral recordings, the blending of pictures, or the quick change fromone tape recording to another.

FIGURE 19 shows disk 26 scanning tape 24 at an angle. This inclinedscanning is intermediate between the type of scanning shown in FIGURES 1and 2 and that shown in FIGURE 18. The curvature of the-tape is reducedas the angle of the wheel from perpendicular is increased.

Variations in the type of magnetic heads, the circuits for recording andreproducing, the contacts between the wheel and the stationary circuitsand other variations may readily come to mind herewith. This recordercan be adapted to record sound or information at very slow tape andscanning wheel speed simply by providing a-slow speed drive; forexample, motor 60 could be replaced with a gear motor. This recorder canbe developed for use in conjunction with a TV camera for recordingpictures for later broadcast or for direct replay on individual TVreceivers.

Magnetic tape is also called magnetic film especially when used in 16and 35 mm. sizes. The word magnetic tape is herein meant to includemagnetic film.

Although I have shown and described only one form of recorder,togetherwith a few variations of the method of scanning, embodying myinvention, it is understood that various changes, modifications, andadaptations may be made therein within the scope of the appended claimswithout departing from thespirit and scope of my invention.

Whatis claimed is:

1. In a magnetic tape recorder, at least one transducer unit, meansserving to carry said unit for rotation, motor means rotating the unitat a constant speed, tape transport means for moving the tape fromoneside to the other of the plane of rotation of the unit, means forrendering said tape transport means operable and inoperable, guide meansfor said tape including guide block having a concave surface with aradius substantially the same as the scanning path of the transducerunit, said surface having a recess therein which extends along thescanning path of the rotating Vtransducer unit, a projection on saidguide block for supporting an edge of said tape to prevent transversemovementjofsaid tape as a result ofthe movement of said transducer unitagainst said tape, means for mounting said guide block for movement froma position wherein the concave surface of said guide block maintainssaid tape in contact with the rotating transducer unit to a positionspaced from the transducer unit, and means for maintaining said guideblock in said first mentioned position When said tape transport means isrendered operable and in said second mentioned position when said tapetransport means is rendered inoperable.

2. In a magnetic tape recorder as claimed in claim 1 wherein themounting means pivotally mounts the guide block and a spring means isprovided for biasing the guide block toward the transducer unit.

References Cited by the Examiner UNITED STATES PATENTS 1,707,243 4/1929'Wildhaber 179-100.2 2,245,286 6/1941 Marzocchi 179-1002 5 2,750,449 6/1956 Thompson 179-1002 3,099,709 7/ 1963 Barry 274-11 BERNARD KONICK,Primary Examiner.

10 J. BREIMAYER, Assistant Examiner.

1. IN A MAGNETIC TAPE RECORDER, AT LEAST ONE TRANDUCER UNIT, MEANSSERVING TO CARRY SAID UNIT FOR ROTATION, MOTOR MEANS ROTATING THE UNITAT A CONSTANT SPEED, TAPE TRANSPORT MEANS FOR MOVING THE TAPE FROM ONESIDE TO THE OTHER OF THE PLANE OF ROTATION OF THE UNIT, MEANS FORRENDERING SAID TAPE TRANSPORT MEANS OPERABLE AND INOPERABLE, GUIDE MEANSFOR SAID TAPE INCLUDING GUIDE BLOCK HAVING A CONCAVE SURFACE WITH ARADIUS SUBSTANTIALLY THE SAME AS THE SCANNING PATH OF THE TRANSDUCERUNIT, SAID SURFACE HAVING A RECESS THEREIN WHICH EXTENDS ALONG THESCANNING PATH OF THE ROTATING TRANSDUCER UNIT, A PROJECTION ON SAIDGUIDE BLOCK FOR SUPPORTING AN EDGE OF SAID TAPE TO PREVENT TRANSVERSEMOVEMENT OF SAID TAPE AS A RESULT OF THE MOVEMENT OF SAID TRANSDUCERUNIT AGAINST SAID TAPE, MEANS FOR MOUNTING SAID GUIDE BLOCK FOR MOVEMENTFROM A POSITION